JP4704763B2 - A method of optically cutting a dome-shaped surface within a substance. - Google Patents

Description

  The present invention generally relates to an apparatus and method for optically cutting a preselected pattern of parenchyma. In particular, the present invention relates to optically cutting a substantially dome shaped layer of corneal tissue using a femtosecond laser. The invention is particularly useful for forming a flap that can be used to correct the refractive properties of the cornea as part of the LASIK process, but is not so limited.

  In the usual LASIK method (Laser In-Situ Keratomeleusis), the patient's cornea is dissected using a microkeratome to form a flap. The flap is then lifted and the cornea After exposing the parenchyma floor, the floor is removed using an excimer laser, and there are some disadvantages to forming a flap using a mechanical instrument such as a microkeratome. For example, when an appropriate flap is formed with the incision blade, the degree to which the surgeon's skill and the cooperation between the eye and the hand are greatly affected. Or, if the flap is completely removed from the cornea, complications can occur, and in addition, incisions are often not possible when using a microincision knife. As a result, when the flap is lifted, the exposed tissue floor will contain an irregular surface, which may cause wrinkles if the flap is returned again. These wrinkles can cause undesirable vision loss.

  Another disadvantage is that the microincision incision is usually not substantially dome-shaped or parallel to the anterior cornea. Because the exposed tissue floor is not parallel to the anterior cornea, the laser removal step is more complex and often difficult to control, so that removal is somewhat inconsistent with the natural curvature of the cornea. It becomes uniform. This is particularly problematic when it is desired to remove a uniform thickness of tissue to correct an eye defect. For example, the removal of a uniform volume of tissue is typically required for myopia, which is commonly seen among adults.

  As an alternative to using a micro incision, a laser is used to form a flap in the LASIK process. For example, a series of laser pulses having a pulse duration in the femtosecond range can be directed to a focal point at a predetermined site in the patient's cornea to photocut the focused tissue accurately and precisely. Tissue photocutting with a femtosecond laser is obtained by a process called laser induced optical destruction (LIOB). In particular, in LIOB processing, optical breakdown occurs at the focal point of the laser due to the generation of extremely high local field strength. As a result of this electric field exceeding the binding energy of the valence electrons with atoms, a microplasma, bubbles and shock waves are generated.

  An example of a process for focusing a pulsed laser beam onto a predetermined subsurface site in the patient's cornea is the “Method for Restoring the Eye” issued to Bill et al. U.S. Pat. No. 4,907,586. The patent discloses the use of a pulsed laser beam for subsurface light cutting of tissue in the corneal stroma in relatively detail. Unlike the excimer laser used after flap formation in the conventional LASIK process, the pulsed laser beam penetrates the corneal tissue and converges to a point below the corneal surface, as disclosed by Bill, and optically cuts the focal corneal tissue. it can.

  Since the pulsed laser beam can reach a subsurface site without necessarily providing a physical passage, it can cut a volume of complex corneal tissue while minimizing the total amount of tissue cut. To form such a shape, the laser beam is first directed (using a suitable optical element including a cutting lens) to the focal point of the target site corresponding to one point of the target volume to be optically cut. After emitting at least one pulse to the focus to remove tissue, the focus is moved (ie, scanned) to another point in the designated volume. At this new site, at least one pulse is issued and the scanning and removal process continues until the entire specified volume of tissue is photocut.

  What is clear from the above description is that the accuracy, agility, and speed of the scanning sub-device greatly affect the performance of the entire surgical device. In other words, the scanning device must be capable of moving the focus accurately and very quickly from one designated site to another. This requirement for the scanning device is particularly important when scanning is required in all three dimensions (ie, movement from one site to the next is simultaneously in the x, y, z directions). In one technique developed to simplify this requirement, the scanning device scans only in two directions perpendicular to each other (rather than in three directions). With this technique, the cornea is first applanated and does not require a scanning motion in the z direction. In that case, the front of the cornea is first adapted to a substantially flat applanation lens. The planar volume of subsurface tissue parallel to the applanation lens is then removed. By using a special cutting lens with no field curvature, the planar volume can be removed only by two-dimensional scanning (ie, scanning at right angles to the applanation lens surface is not necessary). However, as will become apparent later, this technique can produce some serious undesirable consequences.

  Scanning is simple, but flattening the cornea may produce undesirable results. For example, corneal flattening is extremely uncomfortable for the patient. In addition, the intraocular pressure can rise to a dangerously high level. Finally, perhaps equally as important, significant flattening of the cornea can cause strain in the three-dimensional structure of multiple thin layers of the cornea. As a result of this distortion, if the cornea is decompressed after incision with the cornea remarkably flattened, an unpredictable shape change occurs.

  When scanning is performed in three directions perpendicular to each other, several factors can affect device performance. Among these factors is the scan distance required for the focus to move from one removal point to the next. As this scan distance increases, a longer scanning motion is required. As recognized by the present invention, scanning accuracy typically corresponds to scanning distance. Therefore, the scanning accuracy is improved by shortening the scanning distance. Furthermore, longer scanning movements often result in increased wear on the components of the scanning device. This wear often shortens the life of the scanning device. Finally, a short scanning movement can be performed more quickly than a long scanning movement. Therefore, the removal scanning pattern that is desirable to use is a pattern that speeds up the process by minimizing the scanning motion between multiple sites that are successively removed. In some simplification, for a given scan response time, shortening the scan motion can increase the laser pulse repetition rate and, as a result, reduce the overall processing time.

  In light of the foregoing, an object of the present invention is to provide an apparatus and method suitable for the purpose of removing, by light cutting, subsurface sites having a relatively complex shape, such as a substantially dome-shaped corneal parenchymal tissue layer There is to get. Another object of the present invention is to obtain a method of forming a flap that can be used as part of a LASIK process, in particular a flap that exposes a removal surface substantially parallel to the natural front surface of the cornea. Yet another object of the present invention is to provide a method for optically cutting a preselected tissue volume by a series of relatively short scanning motions. Yet another object of the present invention is a method for photocutting corneal parenchyma at multiple focal points below the surface, which is easy to use, relatively simple to implement, and relatively cost effective. It is in.

The present invention is directed to an apparatus and method for optically cutting a preselected corneal tissue volume. One application of the present invention is to remove a substantially dome-shaped subsurface parenchyma layer using a focused laser beam. By this method, a corneal flap can be formed and used as part of the LASIK process to correct the refractive properties of the cornea.
According to one embodiment of the present invention, the disclosed method begins by identifying each of a plurality of sites in the cornea by x, y, z coordinates. In particular, by identifying the coordinates, light is cut at each site, and as a result, a preselected volume is light cut. Usually, coordinates are specified by first forming a two-dimensional planar point pattern, and then converting the planar point pattern into a three-dimensional non-planar pattern. For example, in order to specify coordinates for optically cutting a dome-shaped layer, a planar point pattern such as a two-dimensional spiral line is first formed (for example, in xy space). Next, the z component (z direction is perpendicular to both the x and y directions) is added to each point in the planar pattern, whereby the planar pattern is converted into a set of three-dimensional coordinates.

  Once the coordinates of the light cutting site in the cornea have been identified, the next step is to generate a focused laser beam and scan the focal point of the laser beam from one site to the other in the cornea. For this purpose, a laser device with a laser light source, a laser scanning device, and one or more optical elements are used. According to one configuration, the laser device includes, in order, a laser light source, a laser scanning device for three-dimensional scanning, a plurality of lenses arranged as a telescope, a mirror, and a cutting lens. In some embodiments, a contact lens is used to stabilize the cornea with respect to the laser light source and to match the front of the eyeball to a preselected radius of curvature R. Typically, this radius of curvature R substantially matches the natural radius of curvature of the anterior cornea and is in the range of about 7.5 mm to about 11.0 mm. In most cases, a radius of curvature of about 8.8 mm is utilized. The laser beam is generated by the cooperation of the above-described configuration, and is focused on one of a plurality of predetermined sites in the cornea via the scanning device, the optical element, and the contact lens.

  A series of laser scanner positions are calculated to photocut the corneal tissue at each site. The input data for the scanner position calculation can include the optical properties of the optical elements (ie, the telescope, mirror, cutting lens in the arrangement) and the contact lens (if used). Among other things, this input data can include multiple paths of optical properties through the optical element and the contact lens. The calculated series of laser scanner positions are then used to move the laser beam focus from one site to another, and a preselected tissue volume is photodissected.

  In another aspect of the present invention, a method is provided for optically cutting one surface at a substantially constant distance from the front of the eye within the eye. In this method, a reference frame including a rotation axis (for example, an optical axis of the eye) is provided on the eye. Next, the focal point of the laser beam is positioned at a radial distance r from the axis of rotation within the substance. At least one laser pulse is emitted to this focal point in the parenchyma where the tissue is photocut and a photo-cut bubble having a diameter d is generated. After the light cutting of the first part, the focal point is rotated about the rotation axis by an arc length substantially equal to the angle θ and the diameter d. The photocleavage step is then repeated. As this light cutting is continued, the distance between the focal point and the rotation axis is gradually reduced at a rate equal to the diameter d for each revolution (that is, Δr / rev = d / rev). Furthermore, by controlling the z component, the surface at a certain distance from the front surface of the eye is optically cut. Normally, both the angular rotation speed w and the radial speed of the focus increase as the focus approaches the axis of rotation.

BRIEF DESCRIPTION OF THE DRAWINGS The novel features of the present invention and the present invention itself may be best understood by referring to the accompanying drawings in terms of both construction and operation. In the drawings, similar parts are denoted by similar reference numerals.
FIG. 1 shows an ophthalmic laser device for optically cutting (substantially by a laser-induced optical destructive effect) the subsurface, and is indicated by the reference numeral 10 as a whole. As shown in FIG. 1, the apparatus 10 includes a laser light source 12 that generates a pulsed laser beam and directs the laser beam along a first beam path 14. Typical examples of laser light sources include any solid state fs laser having a pulse duration of 1 fs to about 100 ps, a near infrared operating wavelength, and a repetition rate of 1 to 100 kHz.

Still referring to FIG. 1, it can be seen that the laser beam generated from the laser light source 12 is directed along the beam path 14 and reflected using a 45 ° mirror 16. From the mirror 16, the laser beam is directed to a plurality of lenses configured as a Galilean telescope 18. The laser beam is magnified twice in the telescope 18 (some configurations are magnified three times) and advanced to the master shutter 20. The master shutter 20 functions as a safety component. After passing through the master shutter 20, the laser beam is incident on the scanning unit 22.
The scanning unit 22 typically includes a fixed plano-convex lens that is spaced from the movable plano-concave lens along the laser beam path and the z-axis position of the laser beam focus (the z-axis is that of FIG. 2). Control). The plano-concave lens can be moved using a voice coil (not shown). In addition, the scanning unit 22 includes an xy scanning device having a galvanometer mirror.

A more complete description of a suitable scanning unit and its operation is a commonly owned US patent application entitled “Beam Steering System for Corneal Laser Surgical”. No. 10/821402, which is hereby incorporated by reference in its entirety.
In the case of device 10, the control signal is sent to a unit processor (not shown) where it is processed, for example, by a real-time operating device and evaluated by a suitable hardware device. If an error occurs in the laser output or position adjustment during processing or calibration, the master shutter 20 is activated to shut off the laser beam and prevent damage to the patient's eye due to radiation.
Further, it can be seen from FIG. 1 that the laser beam enters the cutting lens 24 after exiting the scanning unit 22. Specifically, as shown in the figure, the laser beam first passes through a plurality of lenses 26 configured as a telescope, and is then reflected by a 45 ° dichroic mirror 28. The dichroic mirror 28 allows observation of the patient's eye 30 through the mirror 28 and the cutting lens 24 with a microscope (not shown).

  1 and 2, it can be seen that the device 10 includes a contact lens 34. The contact lens is usually made of transparent PMMA and is formed to have a rear surface 36 and a front surface 38 to stabilize the cornea relative to the cutting lens 24. As best seen in FIG. 2, the rear surface 36 of the contact lens 34 is formed to have a substantially constant preselected radius of curvature R. Further, as shown in the figure, the contact lens 34 is disposed in contact with the cornea 32, and the front surface of the cornea 32 has the same shape as the rear surface 36 of the contact lens 34. Usually, the curvature radius R is about 7.5 mm to about 11.0 mm. In most cases, a radius of curvature of about 8.8 mm is used (this curvature is close to the natural curvature of the outer cornea surface). The contact lens 34 prevents the cornea 32 from being significantly flattened.

  Fixation and alignment of the patient's eye 30 is performed by a contact lens 34 and a conical spacer (not shown). For this purpose, the contact lens 34 is applied and held against the eye 30 using a suction cone (not shown) attached to the lens 34. When centered on the eye, the suction cone is fixed by being evacuated. A conical spacer is then placed between the laser beam exit of the cutting lens 24 and the conical spacer. Using an electric patient chair, the eye 30 and the suction cone are moved toward the conical spacer. The connection between the suction cone and the conical spacer is self-centering so that proper xy alignment is maintained. In addition, this configuration provides the correct z distance between the patient's eye 30 and the cutting lens 24. A pressure sensor (not shown) is used to measure the pressure applied to the eye upon contact between the conical spacer and the suction cone. A more complete description of the fixation and alignment device and its operation can be found in Applicant's own concurrent “Device and Method for Positioning a Patient in the Case of Laser Surgery” (System and Method for Positioning a Patient for Laser). No. 10/790625, entitled “Surgery,” which is incorporated herein by reference in its entirety.

  The cornea 32 shown in FIG. 2 is partially separated (ie, incised) to form a flap 42 for LASIK processing. As shown, the incision to form the flap 42 includes a substantially dome-shaped flap floor cut 44 and an edge cut 46 that partially surrounds the floor cut 44 and lifts the flap 42. In order to return it to its original position, a “hinge” is left behind.The edge cut 46 is cut at an edge angle 48 relative to the anterior surface of the cornea 32, which is usually as shown. Slightly below 90 degrees, the flap floor cut 44 is usually made in a substantial portion of the cornea 32 and defines a flap thickness 50. In the case of a typical flap 42 for LASIK processing, the flap thickness 50 is generally about 140-200 μm and the flap bed diameter is about 5.5-10.0 mm As noted above, in some use cases, the flap bed cut 44 is parallel to the front surface 40 of the cornea 32. Formed Rukoto is preferred, therefore, in the illustrated arrangement, it is preferred that the flap floor cutting portion 44 follows the contour of the rear surface of the contact lens 34.

  In one embodiment of the apparatus 10, the flap floor cut 44 is formed by first identifying multiple focal sites within the cornea 32. In particular, by specifying the focal site, a predetermined volume is excised by optical cutting of each focal site. FIG. 3 shows a pattern of bubbles 52 generated as a result of light cutting at a plurality of focal points. The bubbles 52 shown in FIG. 3 are combined to form a dome-shaped incision (that is, the flap floor cutting part 44 shown in FIG. 2). Usually, the set of focal points is specified by forming a two-dimensional planar spot pattern. In the case of the pattern of bubbles 52 in FIG. 3, the initial planar spot pattern is formed in a spiral shape. In one embodiment, the focal spot spiral pattern can be estimated from an Archimedean spiral combined with an I-parameter representation. Specifically, the Archimedean spiral can be estimated from one point that moves at a constant angular velocity or a constant radial velocity. As a result, the spiral arm will have a certain distance. In general, it is desirable that the spots be equally spaced both in the radial direction and in the spiral path. This means that the angular velocity and radial velocity are not constant. In other words, both speeds must be higher at the periphery at the center of the spiral (ie, I parameter display).

Next, the planar spot pattern is converted into a three-dimensional non-planar spot pattern. It can be seen by comparing FIG. 3 with FIG. 4 that the z-component is added to each spot of the planar pattern, thereby transforming the planar pattern into a set of three-dimensional coordinates. The set of coordinates defines the part to be light-cut individually, and the dome-shaped volume is light-cut.
Once this set of coordinates is identified, the apparatus 10 shown in FIG. 1 is used to generate a focused laser beam and scan the focal point of the beam from one site in the cornea 32 to another. For this purpose, a series of laser scanner positions are calculated, the focal point is moved along a path in the cornea, and the corneal tissue is photocut sequentially at each site corresponding to one of the specified coordinates. . In the case of device 10, the position of each laser scanning device in the series includes the tilt angle of each galvanometer mirror and the distance between the fixed plano-convex lens and the movable plano-concave lens.

In the calculation of each laser scanning device position, the input data includes the optical characteristics of one or more optical elements disposed between the scanning unit 22 and the cornea 32. In the case of the apparatus 10 shown in FIG. 1, these optical elements include a lens 26, a mirror 28, a cutting lens 24, and a contact lens 34. For example, the refraction at the interface between the contact lens 34 and the cornea 32 and the refraction at the interface between all other scanning units 22 and the contact lens 34 can be used for calculation as input values.
Furthermore, the calculated input data may include optical characteristics of a plurality of paths passing through an optical element disposed between the scanning unit 22 and the cornea 32. Once calculated, a series of laser scanning device positions are used to move the focal point of the laser beam from site to site within the cornea 32 to optically cut a preselected tissue volume.

  In one embodiment of the apparatus 10, the light cutting of the dome-shaped volume is performed in a unique manner. In particular, in this embodiment, a reference frame having a rotation axis 54 is set for the cornea 32 as shown in FIG. For example, the rotation axis 54 can coincide with the eye axis of the eye 30, and the visual axis of the eye 30 can be arbitrarily selected. Next, the focal point of the laser beam is positioned at a radial distance r from the axis of rotation 54 within the substantial body. Further, referring to FIG. 3, at least one laser pulse is emitted to the focal parenchyma, and the tissue is optically cut to generate a light cut bubble 52a of diameter d. After the light is cut at the first part, the focal point is rotated about the rotation axis 54 by an angle θ in the arrow direction 56. This rotation moves the focal point by an arc length 58 substantially equal to the diameter d. The light cutting step is then repeated (eg, light cutting bubble 52b). During this rotation, the distance between the focal point and the axis of rotation 54 is reduced at a rate substantially equal to the distance d (d / rev) for each revolution.

  Thus, as shown in FIG. 3, after each full rotation, radius r decreases by distance d. This is the same for any bubble. For example, the bubble 52c is separated from the bubble 52d by a distance 60 of about d in the radial direction. Further, during rotation, the focal point moves toward the front surface 40 of the cornea 32 (see FIG. 2), thereby forming a dome-shaped contour. The focal movement of the cornea 32 to the front surface 40 is performed once per revolution, with each focal movement, or at some other preselected rate. As indicated by arrow 56, the focal point moves from the periphery of the dome-shaped surface to the center of the dome-shaped surface. As a result, a light cut surface having a substantially constant distance from the front surface 40 of the cornea 32 is formed.

  Although the particular apparatus and method for optically cutting a dome-shaped surface within the corneal stroma shown and disclosed in detail herein can fully achieve the objectives of the present invention and obtain the aforementioned advantages, They are merely the presently preferred embodiments of the invention and no limitation is imposed on the details of construction or design shown herein other than as described in the claims.

1 is a schematic diagram showing the main optical elements of an apparatus for optically cutting a preselected volume of corneal tissue. The expanded sectional view of the cornea cut in order to form the flap for LASIK processing. Schematic showing a suitable light cut bubble pattern for forming a flap for LASIK processing. FIG. 3 is an enlarged cross-sectional view of the cornea of FIG. 2 showing a suitable light-cutting bubble pattern for forming a LASIK processing flap.

Claims (3)

An apparatus for optical cutting the surface of substantially constant distance from the front of the corneal stroma of the eye, the device is adapted to set a reference frame having a rotation axis to the corneal stroma, the apparatus comprising:
An optical element for positioning a focal point of a laser beam within the cornea in a radial distance from the rotation axis;
A laser light source for optically cutting tissue at the focal point to generate bubbles having a diameter d;
The focal point is rotated about the rotation axis while increasing the rotation speed over an arc length substantially equal to the diameter d, and is substantially increased according to the increase in the rotation speed by a distance d per one rotation. And a scanning device that reduces the distance from the axis of rotation to the focal point at an equal rate.   The light cutting device according to claim 1, wherein the device further includes optical means for moving the focal point in a direction substantially parallel to the rotational axis while the focal point rotates about the rotational axis. The apparatus further includes a contact lens configured to have an anterior surface and a posterior surface, the posterior surface having a radius of curvature R, and the contact lens aligns the anterior surface of the cornea with the posterior surface of the contact lens. The optical cutting device according to claim 1, wherein the optical cutting device is for contacting the corneal stroma .

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